1. Field of the Invention
The present invention relates to an athermal arrayed waveguide grating and, more particularly, to an arrayed waveguide grating capable of compensating wavelength changes according to variations in ambient temperature.
2. Description of the Related Art
With a recent burst of growth of various data services in the Internet field, there has been an increase in demand for higher transmission capacity. The current demand does not seem to slow down in any foreseeable future. The best economical plan of meeting this demand is to maximize the transmission capacity in the existing optical fibers. For example, an optical communication system is operated in a wavelength-division-multiplexing (WDM) mode in which a plurality of channels can be transmitted/received through a single optical fiber as one communication line, instead of installing additional optical fibers on a large scale. This type of optical-communication system was commercialized in 1995 for the first time, and since then the available transmission/reception capacity has been improved remarkably.
In the WDM systems, an optical device, such as an arrayed waveguide grating in which an optical waveguide is formed on a flat plate of silica by a combination of fiber optic technology with a large-scale-integrated (LSI) circuit technique, is used as a wavelength-division multiplexer/demultiplexer for allowing multiple wavelengths to be combined and separated for transmission/reception applications. However, the arrayed waveguide grating is sensitive to temperature change which in turn changes its refractive index according to the temperature changes. As a result, optical signals inputted into the arrayed-waveguide grating are subjected to a change in the phase, thereby causing a wavelength sweep.
In general, the arrayed-waveguide grating (AWG) includes an input waveguide, a grating array, first and second slabs, and an output waveguide array, and functions as a wavelength-division multiplexer/demultiplexer in which optical signals inputted from the outside are not only demultiplexed into a plurality of channels having different wavelengths but also multiplexed into one channel, and then outputs the multiplexed/demultiplexed resultant(s). The AWG may further include a temperature controller, thus preventing a wavelength sweep of outputted channel(s) caused by a change in ambient temperature. The temperature controller typically includes a heater device or a peltier device. An isothermal plate of copper, for instance, may also be inserted between the AWG and a heater or peltier device.
In operation, the input waveguide inputs external optical signals into the first slab. The grating array separates the inputted optical signals into different light wavelengths. The first slab connects the input waveguide with the grating array. Meanwhile, the second slab allows the separated wavelengths of light to be imaged on its egress surface. Further, the output-waveguide array allows each wavelength of light, which is imaged on the egress surface of the second slab, to be outputted to the outside in the form of a separated channel.
The AWG or waveguide module including the heater or peltier device as mentioned above is disclosed in the International Patent Application No. PCT/JP2001/00352 to Hiro Yoshiyuki, et al., entitled “Heater Module and Optical Waveguide Module,” the teachings of which are hereby incorporated by reference.
Briefly, the AWG includes the temperature controller, so that the AWG suppresses a change in the phase of an optical signal caused by the temperature change as well as the wavelength sweep of each output channel. That is to say, the temperature controller allows the AWG to maintain a constant temperature, so that each output channel can be prevented from being swept in wavelength, thereby enabling the AWG to obtain a stable performance characteristic. However, because the conventional AWG employs a heater or peltier device as the temperature controller, the AWG must be always heated during operation. As a result, a power consumption for the AWG is increased. In addition, there are other drawbacks in that the prior art AWG which includes an increased volume, a complicated assembly process, an increased manufacturing cost, and so forth.
Accordingly, there is a need for an improved arrayed waveguide grating that is not sensitive to variations in ambient temperature that may be realized in a simple, reliable, and inexpensive implementation.